The general theory of stereotactic neurosurgery is that if an arc is formed alongside the patient's head any trajectory passing through this arc at a right angle to the arc will always meet at the central point of the arc. Employment of this theory enables localization of any point within the head. However, when examining present stereotactic equipment, the most striking feature is that in spite of tremendous advancement in scanning techniques and the effective arc principle, the present stereotactic frames are very complicated and difficult to maneuver.
Most of the present equipment requires fixation of the stereotactic frame to the patient's head before scanning is performed. Screws or head pins are used to secure the stereotactic frame to the patient's head. Since the frame must be left on the patient's head from the time of scanning until the time of the surgery, the scanning must be done the morning of the surgery. This naturally delays the neurosurgical procedure. In practical terms, every stereotactic procedure will take about three (3) to four (4) hours of a neurosurgeon's morning because of this inconvenience.
In addition, when using stereotactic devices which require pinning the whole frame to the patient's head it is extremely difficult to localize lesions of the posterior fossa. Localizing lesions of the posterior fossa requires the neurosurgeon to reverse the whole frame. This is an extremely cumbersome procedure and very often is not practical.
There is a need for a stereotactic frame and localization method which utilizes naturally occurring cranial reference points which can be accurately and consistently reproduced when the stereotactic frame is secured to the patient's head at the time of surgery. Applicant's invention meets this need since it enables scanning anytime before surgery without securing the whole stereotactic frame to the patient's head and allows for accurate and consistent reproduction of the cranial reference points at the time of surgery.